Light emitting diode (LED) technology is a maturing technology that continues to show improvements in efficiency, customability and cost reduction. LED technology is rapidly being deployed in a host of industries and markets including general lighting for homes, offices, and transportation, solid state display lighting such as in LCDs, aviation, agricultural, medical, and other fields of application. The increased energy efficiency of LED technology compared with other lighting solutions coupled with the reduction of costs of LED themselves are increasing the number of LED applications and rate of adoptions across industries. While LED technology promises greater reliability, longer lifetimes and greater efficiencies than other lighting technologies, the ability to mix and independently drive different color LEDs to produce customized and dynamic light output makes LED technology and solid state lighting (SSL) in general robust platforms to meet the demands of a variety of market needs and opens the door to many new applications of these lighting technologies. The ability to tailor and tune the output spectra of LED fixtures and dynamically switch individual LEDs “on-the-fly”, for example in response to an environmental cue, dramatically opens up the application space of solid state lighting.
As is well known in the art, LED luminaires generally comprise one or more individual LEDs dies or packages mounted on a circuit board. The LEDs may be electrically connected together on a single channel or be distributed and electrically driven across multiple independent channels. The LEDs are typically powered by current from an associated LED driver or power supply. Examples of these power supply drivers include AC/DC and DC/DC switched mode power supplies (SMPS). Examples of LED power drivers include power supplies designed to supply constant current to the LED string in order to maintain a consistent and steady light output from the LEDs. LEDs may also be powered by an AC power source. Direct AC power typically undergoes rectification and other power conditioning prior to being deliver to the LEDs. LED luminaires may also comprise an optic or diffuser, a heat sink and other structural components.
Although LEDs may be combined in such a way to deliver a wide variety of specific color outputs, LED luminaires for general lighting typically are designed to produce white light. Light perceived as white or near-white may be generated by a combination of red, green, and blue (RGB) LEDs. Output color of such a device may be altered by color mixing, for instance varying the amount of illumination produced by each of the respective color LEDs by adjusting the supply of current to each of the red, green, and blue LEDs. Another method for generating white or near-white light is by using a lumiphor such as a phosphor in conjunction with a blue “pump” LED. Still another approach for producing white light is to stimulate phosphors or dyes of multiple colors with an LED source. Many other approaches can also be taken.
Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins, and is found in intrinsically photosensitive retinal ganglion cells (ipRGCs) of humans and other mammals. Melanopsin plays an important non-image-forming role in the photoentrainment of circadian rhythms as well as potentially many other physiologic functions. Stimulation of melanopsin-containing ipRGCs contributes to various reflexive responses of the brain and body to the presence of light. Melanopsin photoreceptors are sensitive to a range of wavelengths and reach peak light absorption at wavelengths around 480-500 (or 490) nanometers (nm). Melanopic light, that is light corresponding to the melanopsin action spectrum, including particularly the wavelengths in the 480-500 nm region is important for non-visual stimuli including physiological and neurological effects such as pupillary light reflex and circadian entrainment and/or disruption. Time coordinated exposure, including over-exposure and under-exposure to melanopic light can be used to entrain and facilitate healthy circadian rhythms in humans and other mammals. When used herein, melanopic light is meant to generally refer to light that stimulates melanopsin and or that may have an effect on human circadian rhythms. When used herein, unless otherwise specified, “melanopic light” is not restricted to a particular or narrow band of wavelengths but rather is meant to mean light that corresponds to or is contained within range of wavelengths that correspond to the that melanopsin action spectrum.
Circadian related photoreceptors are in macular and peripheral vision nearest to the fovea. Melanopsin related photoreceptors are most sensitive in the lower hemisphere of the retina. Selective stimulation of these photoreceptors is possible by directing illumination, and specifically melanopic light, towards or away from the region of the retina where melanopic photoreceptors are most concentrated or most sensitive or responsive. If the desire is to optimally stimulate these photoreceptors, then a light source that produces high biological light (i.e., melanopic light) in this region would be a good solution. Equivalent Melanopic Lux (EML) is a metric for measuring the biological effects of light on humans. EML as a metric is weighted to the ipRGCs response to light and translates how much the spectrum of a light source stimulates ipRGCs and affects the circadian system. Melanopic ratio is the ratio of melanopic lux to photopic lux for a given light source.
The variation of the intensity of light output has a relatively straightforward and understandable effect, namely, higher or lower light intensities incident on the human visual system provide greater or lesser biological stimulation respectively (e.g., with respect to circadian rhythms), the combination of both color variation (e.g., via spectral tuning) and intensity variation can create complementary and in some cases synergistic biological effects. However, spatial distribution is a factor that adds a great deal of complexity and potential cost. Scientific studies have shown that light above the horizon has high biological significance compared with light coming from below the horizon. One consequence of this finding is that illumination emanating (e.g., reflecting) from vertical surfaces (e.g., upper portions of walls and ceilings) has a higher biological significance compared to lower horizontal surfaces (e.g., desktops and tabletops). This differential in biological effect is due at least in part to the fact that there is a greater concentration of melanopsin receptors (ipRGCs) in the lower hemisphere of the human retina than in the upper hemisphere. Thus, the biological effect of light impacting the lower hemisphere of the retina may be greater than the biological effect of the same light incident on the upper hemisphere. This provides an opportunity to further target and optimize biological effects using lighting via spatial distribution and/or spatial modulation of illumination systems, for example by creating layers of light that illuminate different surfaces at different times of day (for example, high vertical illumination during biological daytime, and low vertical illumination during biological night time).